Senbonzakura Violin Motion arm problems.

I'm at a loss with this motion. So there's a reoccurring problem that some users are having with this motion that I'm also having. Basically when this motion is loaded onto the model, the arms barely move and are stuck in the spread position.

This issue has been brought up from what I can find, but most people are either unanswered, while the others have responses that make no sense whatsoever (whether it's language barrier or technical jargon). What I got was is an IK bone arm thing, which I have no clue about.

I started to rough it and just remake new arm motions, even though I know nothing about violin playing, and the result is a huge clusterfuck so far.

I really want to make a video with this motion and song, but with this error and practically no clear way to solve it's all so frustrating.

Short answer is that most likely the motion is made using IK bones for the arms, those bones are not common on MMD models, they can be added, but the amount of motions that use them is very small, so since most likely the model you are using doesn´t have those bones, the motion will never work, unless you add those.